Heretofore, a particle accelerator such as a synchrotron or a cyclotron which accelerates charged particles such as electrons, protons, ions and the like to high energy has been widely known, and recently the application thereof is expanding into other fields such as minute working of semiconductor and medical treatment of cancer.
In a case of a synchrotron accelerator, a track for the charged particles is constructed in the form of a vacuum duct. A plurality of electromagnets are provided along the track to deflect the particles. A device for generating a high-frequency electromagnetic wave is also provided along the track. In the initial stage of the operation, charged particles are supplied to the accelerator at a comparatively low energy, and accelerated by the application of the electromagnetic wave according to a predetermined pattern. In order to deflect the accelerated particles along the track, the current flowing through each electromagnet is varied according to the energy of the particles imparted by the acceleration. When the particles are accelerated to an objective energy, the particles are held in this state for a predetermined time, and then extracted from the accelerator. In order to realize the above current pattern, the control device of a accelerator is equipped with memory devices for generating such patterned signals as mentioned above for the power source of the electromagnet coils and the electromagnetic wave power generator (referred to as an RF hereinafter).
FIGS. 1 and 2 show an example of a conventional particle accelerator control device having such a memory device.
In FIG. 1, the control device 1 comprises a control computer 2, a pulse generator 3 and a memory device 4 whose output signal DO is sent to a power source 5. The power source 5 supplies current I controlled by the output signal DO to an electromagnet coil K of the particle accelerator.
A reference signal of current I flowing through the electromagnet coil K, that is, an objective value, is provided by the memory device 4 as a digital output signal DO. The memory device 4 stores a variation of the current reference signal with time, that is, a running pattern, and reads out a memory content of 1 word for each clock pulse CP produced by the pulse generator 3 and outputs it as the digital output signal DO. A read address of the memory device 4 is increased by an amount corresponding to 1 word for each clock pulse CP. Furthermore, the running pattern stored in the memory device 4 is preliminarily written by the control computer 2 through a data bus 6. Furthermore, the control computer 2 provides a start/stop signal ST to the pulse generator 3 to control a start and stop of generation of clock pulse CP.
FIG. 2 illustrates an operation of the memory device 4. Every time the clock pulse CP is input, an address counter 41 is increased by 1 address and data in this address is read out from a memory 42 and set in an output register 43. The data set in the output register 43 is output as the digital output signal DO.
The data stored in the memory 42 has been written in by the control computer 2 connected to the data bus 6, before the operation begins.
FIG. 3 is a time chart showing a typical operation of the above mentioned device. As shown in this figure, when the start/stop signal ST from the control computer 2 becomes ON, the pulse generator 3 outputs the clock pulse CP continuously. With this clock pulse CP, the memory device 4 starts to output a data having a pattern which becomes the digital output signal DO. A rise portion of the digital output signal DO corresponds to an increase of particle energy during which injected particles of low energy are accelerated to a predetermined high energy state. When it reaches the predetermined energy level, the digital output signal DO becomes a constant value during which the particle is extracted and used according to the object of the accelerator. Thereafter, the start/stop signal ST becomes OFF and the pulse train of the clock pulse CP is stopped, so that the digital output signal DO becomes zero. With this, the current I attenuates with a time constant of a closed circuit formed between the electromagnet coil K and the power source 5. The above operation is usually repeated, which is referred to as "periodic operation", hereinafter.
In this case, operation patterns of sufficiently high precision are required to be stored in the memory device 4 for obtaining a sufficient amount of the extracted particles. That is, when the particles are accelerated according to an operation pattern adjusted insufficiently, the particles tend to be deviated from the predetermined path, and therefore the amount of the highly energized particles extracted from the accelerator is reduced. In order to overcome this difficulty, it is required that the clock pulses CP generated from the pulse generator 3 are set at a high frequency, and the number of data words used for defining the operation pattern must be increased sufficiently. For instance, several hundred kilowords are sometimes required for forming one operation pattern.
Theoretically, the aforementioned operation pattern may be predetermined at a desired extent of precision. However, in a practical case, the pattern tends to deviate from the theoretical value according to the actual condition of the electromagnets and the related circuits. Accordingly, in a conventional accelerator, the required amount of charged particles have been obtained from the accelerator in a manner such that the intensity of the beam of the charged particles is constantly evaluated, and the contents of the memory device storing the operation pattern are rewritten on the basis of the evaluated results.
Furthermore, in a system utilizing the highly energized particles extracted from the accelerator, it is urgently required that the charged particles are obtained in a short period (for instance 1.about.2 sec.). However, since a considerable time is required in rewriting the contents of the memory device storing a large amount of data as described above, it is made essential to interrupt the cyclic operation of the accelerator for a predetermined time. Thus, it is impossible to regulate current rapidly and with high accuracy, resulting in a lowered operation efficiency of the accelerator.